In the prior art, IP networks and other communication systems have provided VoIP (Voice over Internet Protocol) and other telephone services, as well as web page browsing services through access by a web browser and similar.
However, when telephony and web page access are concentrated at one time, cases occur in which the communication system enters a congested state. In such cases, time required to response to communication requests and similar becomes longer, and as a result provision of continuous service becomes more difficult.
The following technologies, for example, address such congested states. That is, a VoIP gateway apparatus transmits a request to a SIP server, measures the time until a response is received, and when the time exceeds a threshold value or similar, judges the SIP server to be in a congested state, and restricts the transmission of new requests to the SIP server.
Further, there is also a technology in which a congestion control apparatus receives a request message for a web server transmitted from a client, and acquires an IP address corresponding to the host name contained in the message from a DNS server. And, based on a congestion management table, the congestion control apparatus judges whether the IP address is in a congested state, and upon judging that the state is a congested state, distributes request messages to web servers with the same host name as the host name, and with different IP addresses which are not in a congested state.
Patent Document 1: Japanese Laid-open Patent Publication No. 2007-312277
Patent Document 2: Japanese Laid-open Patent Publication No. 2006-222631
However, in both of the above-described technologies restriction or other congestion control processing is performed for an SIP server, IP address or similar after congestion has occurred and a judgment of a congested state has been made. Hence neither of the above-described technologies can suppress the occurrence of congestion in advance, prior to the occurrence of congestion.
Further, when among the above-described technologies a technology to restrict transmission of new requests is used, even if a telephone call for restriction has high priority compared with other telephone calls, upon judgment of a congested state, transmission of new requests for the telephone call is restricted. Hence when using such technology there are cases in which a telephone call with high priority compared with other telephone calls cannot be continuously provided.
Also, when among the above-described technologies a technology to distribute request messages to other IP addresses is used, even for example in the case of a web page with high priority compared with others, if an IP address of a web server providing this web page is judged to be in a congested state, distribution to other web servers is performed. Hence when using this technology, there are cases in which, due to distribution of request messages to other web servers, browsing of the web page cannot be continuously provided.